Great video, thanks. Carl Sagan literally changed my life, and is the closest thing I have to a personal prophet. He set such a high standard for humanity that most of us seem petty and prosaic by comparison. I really think he was trying to be a prophet of a new kind of cosmic religion, but sadly even most scientists seem to have missed the message. What science needs desperately in these times of decreasing moral authority is more poets and prophets like Sagan who appeal to the imagination and our higher selves, and fewer uninspiring number crunchers!

When I listen to Sagan speak about Science and Space and how tiny and fragile the Earth is, it makes me think of how intelligent and evolved his mind is, and stupid, infantile, unimaginative, brutish, warlike, etc. all the rest of us humans are. We are doomed. Sorry, Carl.

Timmy @11:
I envision humanity, struggling over oil, over myths, over domination, to be like colonies of ants. We spend generations fighting furiously for inches of territory while huge events unfold over our heads unseen.

I’m interested by the persistence of the “life beyond Earth is likely to exist” meme among people who are otherwise really good at being skeptical and evidence-based, and resistant to the emotional appeal of a seductive myth.

I support SETI. I think it’s very much worth engaging in, as part of generally looking around at things we haven’t previously looked at, and asking questions about what’s out there. And the question “are we alone?” has an undeniable appeal. But from my perspective, too many SETI advocates suffer from what I can only interpret as a fallacious belief in a high probability of extraterrestrial life. I think Carl Sagan suffered from that fallacy.

The Drake equation is an interesting thought experiment, and working to refine the values for the various factors in it strikes me as a worthwhile exercise. But counting galaxies and stars and planets, and statistically assessing the number of potentially Earth-like worlds within a given volume of space, can only take us so far. As long as we lack evidence for even a single case of abiogenesis other than our own, there simply is no way to assign a probability that life beyond Earth exists.

We have two possibilities to choose from: Life came into existence exactly once. Or it came into existence more than once. Each of those possibilities accounts for our own presence as observers. Yes, the astronomically high number of suitable homes for life beyond Earth means abiogenesis would have to have been extraordinarily unlikely for it to have happened only once. But (and here’s the key point) just because it would have to have been “extraordinarily unlikely” for that to have occurred doesn’t mean we get to use that to argue that it is therefore extraordinarily likely (or even likely at all) that life came into being more than once. Anyone who understands the anthropic principle should know that.

I’m as interested as the next person in evidence (like the recent Kepler data) that helps us better assess how common Goldilocks-zone rocky planets and moons are, and I hope I live to see the results of imaging such bodies with big space-based visual interferometers, or sending probes to them and returning detailed information. But I’ll continue to be skeptical of anyone who tries to convince me that he or she can say, based on anything more compelling than a deep-seated emotional desire not to be alone in the universe, that it is _likely_ (the key word) that extraterrestrial life exists. We simply don’t know, and can’t know, based on current evidence, whether it is likely or not.

It’s ironic to me that some of our greatest skeptics, people who dedicated their lives to identifying the childlike emotions that lead many to adopt irrational religious beliefs, would be prone to the same mistake when assessing the likelihood of extraterrestrial life. We needn’t be afraid of the dark. But neither should we let fear of an empty void push us into populating the universe with imaginary beings for which we lack rational evidence.

I love the way Carl Sagan speaks. I feel like I’ve missed out on something amazing in that he passed away before I truly got in to astronomy. Everytime I hear him speaking in it sounds like a truly profound poetic voice of reason that does everything that can be done to drive forth the realms of science and imagination. I wish there was someone following in his footsteps at a time when we’re discovering new and exciting things seemingly every day. I mean there are great astronomers out there like you yourself Phil – teaching the world the about the importance of things beyond this rock, but I just can’t think of someone who could articulate in such a poetic way what it means to LOOK UP and WONDER.

John Callender, I agree that skeptical people need let go of Star Trek fantasies and should be more willing to accept the possibility of a universe without other intelligent life. I can think of at least two reasons why people like Sagan and Clarke were so interested in the discovery of ETI:

One, it would be a mortal blow to Copernican thinking, and especially to our legacy religions. It’s not clear how someone could still take any religion which claims that man was created in the image of God seriously if we encounter a more advanced species that is totally alien.

Two, it would confirm their outlook of “cosmic optimism”. The longer we face a “Great Silence”, the more we’ll worry that the pessimists are right that intelligent life destroys itself before it leaves its cradle. This may be the Lovecraftian darkness that people are most afraid to face – the void of a universe that is fundamentally unfriendly to the cosmic ambitions of intelligent life.

@Cosmist: Those are good points, and provide a more-detailed picture of why SETI advocates might feel an emotional desire to lean on the scales when assessing the probability of ETI’s existence. Of course, that doesn’t make doing so any more rational.

On the blow to legacy religion that discovery of a more-advanced ETI would deliver, I’m not sure it would really make much difference. People who believe that the world will end on a particular date tend to manifest stronger, rather than weaker, belief when that date comes and goes without the world ending. “Our faith is what made God change His mind!” The people who cling today to Copernican cosmology and/or Biblical creationism are doing so in the face of overwhelming evidence to the contrary. I suspect their beliefs will do just fine if ET shows up tomorrow. But it would be interesting to find out.

The Doctor: Almost every species in the universe has an irrational fear of the dark. But they’re wrong, because it’s not irrational. It’s Vashta Nerada.
Donna: What’s Vashta Nerada?
The Doctor: It’s what’s in the dark. It’s what’s always in the dark.

John Callender, I understand your point but still agree with the way Sagan phrases things (despite his obvious optimism). It doesn’t make sense (to me, at least) to hinge your probabilistic distribution between “one instance of life” and “more than one instance of life” as you propose; rather, I’d say that there either is or isn’t life on any given world. That seems more logical and makes the statistics roughly a million times easier. Because we are here, it is safe to assume the odds of life happening are nonzero. From there, even an unimaginably slight chance of life occurring leads to many instances of life throughout the cosmos. This is a simple argument from probability, and Carl Sagan presents it as such. There is a chance that we are the only ones, but without any more knowledge about the distribution of life, nothing more can be said one way or the other.

The odds of us being singular, however, will always be lower than a case of multitudes. Think of the singular case (us, alone) as the tail end of any continuous distribution. I don’t think this as dependent on belief as you say it is.

Kevin Brennan, I think the probabilities are tricky to assess, and “seems more logical” is a dangerous guide. “Because we are here, it is safe to assume the odds of life happening are nonzero.” Yes, that’s true, but it’s also a tautology: If we lived in a universe without life, we wouldn’t be living there to make the observation. By definition any universe in which we are present to discuss the question is a universe in which life has emerged at least once.

“From there, even an unimaginably slight chance of life occurring leads to many instances of life throughout the cosmos. This is a simple argument from probability…” I think it is a fallacious argument from probability. It is only _some_ unimaginably slight chances that lead to many instances of life occurring. For any given universe having a particular (very large) number of opportunities for life to emerge, it is possible to imagine a probability of life’s emerging that is so unimaginably small that the event will happen only once.

Which universe do we live in: The one where the chances of life emerging are large enough for it to have happened more than once? Or the one where it is so rare that it happened only the one time? Until we find a second instance of life’s emergence, we have no way of assigning a probability.

Let’s say you found yourself standing in the street holding a winning lottery ticket. If you knew how many others had bought tickets, but you didn’t know the actual odds of winning, could you calculate the probability that there were other winners besides yourself?

I don’t think you could. You seem to acknowledge this when you write, “There is a chance that we are the only ones, but without any more knowledge about the distribution of life, nothing more can be said one way or the other.” Yes, that is exactly my point. But you contradict that when you try to assign probabilities, as you appear to do when you say that “even an unimaginably slight chance… leads to many instances of life” and “the odds of us being singular… will always be lower than a case of multitudes.”

As lottery winners, we know the odds of winning must be greater than zero. But that’s all we know. If we want to make probabilistic assertions about how many other lottery winners are out there, we will need to gather more data. I’m all for gathering that data. In the meantime, though, we don’t actually know how likely or unlikely it is that other winners exist. And I think it is logically suspect to pretend that we do.

Such a great voice – really makes you pay attention to every word. I’m sure it’s been said many times but he was the consummate communicator – sadly missed. And the music fits so well too. Thanks for sharing

John I agree with a lot of what you say. Lots of people I know take a passing interest in astronomy, particularly the search for exo-planets and SETI, and will want to spark up a conversation about this sort of thing when I tell them I’m studying astronomy. Most people however seem to suffer from the same ailment as the taxi driver that Sagan talks about early in The Demon Haunted World. They have the sense of wonder and willingness to learn about the universe, but are unable to separate the wheat from the chaff having never been taught the importance of scepticism in a world surrounded with mysticism.
So when we arrive at an issue like ET, it does seem to the layman that if there are billions and billions of worlds out there like those astronomers tell us then there must be at least one other inhabited planet out there. Even to someone who may otherwise call them selves a sceptic the prospect is so great that many emotions are involved. Of course you and I know that with life on Earth as our single data point we can’t possibly know anything like the odds of life arising on any world.
All we can do is use the tantalizing data that we have from kepler etc to keep on inspiring others to take an interest in the question, all the while reminding them of the importance of the tools of science and scepticism in the search for an answer. To me, that’s what Carl Sagan was all about.

Yes, the astronomically high number of suitable homes for life beyond Earth means abiogenesis would have to have been extraordinarily unlikely for it to have happened only once. But (and here’s the key point) just because it would have to have been “extraordinarily unlikely” for that to have occurred doesn’t mean we get to use that to argue that it is therefore extraordinarily likely (or even likely at all) that life came into being more than once. Anyone who understands the anthropic principle should know that.

Even the first part is a false inference, because of the Anthropic Principle. Life could be quite likely in theory, yet still we’re the only place that it happened in the visible universe; that’s just the way the odds turned out. Maybe other parts of the universe are stuffed with life, and we’re an outlier.

Let’s say you found yourself standing in the street holding a winning lottery ticket. If you knew how many others had bought tickets, but you didn’t know the actual odds of winning, could you calculate the probability that there were other winners besides yourself?

If I was holding a winning lottery ticket, I could, depending on the game, figure out quite a bit about the probability of winning, and thus the likelihood of other winners. Sure if it was nothing but a scratch off that said either “you win” or “you lose” then I wouldn’t know anything. But if there was some indication on the ticket as to why I won, like a number of symbols that all matched, or a particular sequence of numbers, then I could start to figure out the rules and at least come up with some reasonable bounds.

As lottery winners, we know the odds of winning must be greater than zero. But that’s all we know.

Well, no it isn’t, actually. We do know quite a bit more than that. This is not a case of the “you win” ticket that contains no other information. The ticket, our biosphere and the organisms in it, have many clues.

Do we enough to say we know how likely or unlikely it is? No. But can we reason about it based on information we have and come up with some reasonable constraints? Yes, we can. And basically, while our theories of abiogenesis are anything but complete, nothing in life seems to be particularly exotic, and the chemical reactions not that improbable. Some models have basic organic molecules forming self-replicating membrane structures almost as a matter of course. It just needs liquid water, organics, a source of energy, and time. So it has seemed as though the most likely way in which life would end up being extremely unlikely was if planets with all of those things ended up being unlikely, and Earth was a rarity.

Not looking like that’s going to be the case.

So while it definitely involves speculation, we can still say that life is probably not extremely unlikely, which means it is likely to have arisen more than once.

And so I feel perfectly comfortable saying that I think life beyond earth is likely to exist, and I don’t feel it’s logically suspect as long as I understand the bounds of knowledge used to make that statement.

The great man Carl Sagan’s words always inspire, he puts the human race’s petty squabbles and distractions into perspective. He reminds us that no…humankind is not at the centre of everything. We are in fact just one tiny part of a far, far bigger picture.

I wonder what he would have made of the recent historic exoplanet discoveries by the Kepler Space Telescope. It probably just proved what he knew all along !

Of course we can’t believe in the existence or non-existence of life without evidence. We’re all alien-agnostics. Except looking for alien life is something that is firmly within the grasp of empirical science, and given the question’s appeal (“are we alone?”) and the possibility that it could be answered, a lot of real scientists are certainly going to put effort into trying to answer it. Sagan was one of them, though I don’t think by any means he had a “faith” in aliens the way a lot of people have faith in gods or UFOs or dragons-in-garages despite the absence of evidence.

The thing is, we’ve barely even opened our eyes. The only things we can look for sitting on Earth are high-energy civilizations deliberately messaging us, other information about high-energy civilizations not intended for us, possible biological transformations of other worlds, or as in case of the Kepler Mission, better numbers with which we can slightly refine our plausibility model (the Drake Equation). And with only 50 years or so of searching, we’ve barely taken a drop of water from the cosmic ocean.

There could certainly be life elsewhere if we actually go places and look up-close, which is presently of course not possible except within our solar system (which probably has no other life or at least no complex life outside of Earth). There could be prokaryotic slimes on a million worlds in the galaxy, more complex lifeforms on a thousand. We wouldn’t be able to detect them from here. There could be sentient but low-tech beings elsewhere. We wouldn’t be able to detect them from here. There could be a newly-arisen Type-1 civilization somewhere in the far regions of the Norma arm. We wouldn’t be able to detect them from here.

In any case, with a galaxy of hundreds of billions of stars and (most likely) hundreds of billions of planets and moons, it will be a LONG time before we can say the answer is a firm “No life, we are alone”. And stretch that out to the whole universe and disproving alien life becomes another dozen orders of magnitude harder. So yeah. I think that we’ll *eventually* find a “Yes, there is other life” given the scale of things, provided we (or whatever “we” become in the future) don’t destroy ourselves and keep searching.

I was a colleague of Sagan, albeit a much younger colleague. Your statement that he “inspired millions to look up, to be curious, to wonder” is accurate to be sure. It is odd though, how the collective memory of the masses gets distorted over time. Today, there is a level of adulation for the man that is, frankly, not in proportion to his contributions to scientific understanding. In his day, he was not regarded as a person “at the top” of his field. Many, perhaps even most, of his colleagues considered him to be on the fringe of science. I have not seen much on this in current articles about Carl Sagan, but he had many, many mental and emotional “instabilities”. At the time it was fairly well-known (at least to most of us, and I presume the general public) that he was a prolific user of marijuana. In fact, my personal belief is that is what made him into an icon for the masses, particularly the younger crowd. What is not widely known among the public (then or now) is the various other substances used or abused by Sagan. He was really into the mysteries of the mind, and did things to his own mind in an attempt to ascertain those mysteries. All he succeeded in doing was to scramble things up to the point that no credible scientific body would review or publish his ‘serious’ scientific papers. In person, you could barely follow a conversation, he flitted from topic to topic in mid-sentence, without apparent knowledge that he had done so. If you attempted to reply, he was already three topics over by that time, he stared at you with a blank look, and without understanding what you said or why you said it. You may as well have spoken an alien language. He had major issues with the women in his life, little of it known to the public. In short he was a sad, sad man of little real consequence to the scientific community of the time. His one and only ‘gift’ was the ability to communicate complicated scientific concepts to the less educated public. He believed everyone had the capacity to understand it, if it was presented in less ‘technical’ terms. I believe he was right about that. But rest assured, for most of his career, he was regarded by his peers as not much more than a “kook”. A useful one to be sure, but a kook nonetheless.

However, is still my all-time favourite Carl Sagan quote & clip – with that a fairly close second.

Based on the history of life on Earth, the shortness of the span that Humanity has been around versus the vast aeons where life – non-“intelligent”, certainly non-technological life – has existed with little mind and intellectual contemplation; I suspect that life may be abundant yet sentience vanishingly rare.

The Doctor: Almost every species in the universe has an irrational fear of the dark. But they’re wrong, because it’s not irrational. It’s Vashta Nerada.
Donna: What’s Vashta Nerada?
The Doctor: It’s what’s in the dark. It’s what’s always in the dark.

“It’s not clear how someone could still take any religion which claims that man was created in the image of God seriously if we encounter a more advanced species that is totally alien.”
Irrational beliefs survived harsher things than that. I would not worry about any religions – they will adapt, as they always do. In worst case, people will make up new religions better matching their wishes.

“The people who cling today to Copernican cosmology and/or Biblical creationism are doing so in the face of overwhelming evidence to the contrary.”
What “overwhelming evidence to the contrary” exists for copernican principle? Only one challenge to Copernican principle that I know is Fermi paradox – rest either cannot be assessed due to current technology or is vindicated (currently exoplnets are transisting from first to second).

I know what on I will bet when seeing in the dark beyond our current knowledge.

The construct that we are “The sole event of life in the Universe” does not pass the Ockham’s Razor. Plurality should not be posited without necessity, and the idea that we were the lucky sole life point, is a HIGHLY and twistedly complicated (not complex) pluralistic construct (it is not a theory because it has no evidentiary base). Simplicity in utterance is not the same thing as simplicity in construct, in the Ockham’s sense. To contend that we sit here totally alone in the Universe is a pseudo-scientific religious wish – or in many cases an act of self aggrandizement and argumentativeness.

But be aware that this religious wish, along with hypnotically cocooning yourself inside clans of people all chanting the same thing and stroking each other with self congratulatory praises for being the best, brightest, and smartest,- can also blind you. Empires were lost in the hands of such fools. Be skeptical of even your comfortable familiar surroundings and sayings.

I think that “The Cosmist” got it very wrong and I think Sagan would be pissed that he called him a prophet of some scientific cosmic religeon. Sagan asked that we dont take the words of scientist as facts or beliefs but instead always question and learn through logic and proof for our own understanding and not have blind faith in science.

or maby we should focus on our own planet…….yah the one we are destroying, the monetary value we put on life…. why would any other lifeforms want us around were a virus a plague until we learn to be at one with ourselves and our planet we will always be in the dark!!!!

Hello. I should point out a couple of things, my name is Alan, I just like my nickname. Also, I am a hobbyist astronomer at best, just some guy looking up at worst.

I don’t think the chances of life on another planet is a statistical improbability. I think it’s far more improbable that earth is the only planet in the entire universe that has life. All that’s needed are the right chemical mixes. And even then, it’s possible that our particular mix of elements isn’t the only blueprint for life. The cosmos is filled which such incredible wonders that reach far beyond our spectrum of what can be considered “normal.” I remember hearing about a planet which could have mountains made of diamond (thank you Google, a gas giant called WASP-12b), I almost wept when I considered the size of VY Canis Majoris in relation to my insignificant frame. Yes, it’s optimistic of me to assume that there is life based purely on chance and not on evidence but when you consider that we have barely skimmed the surface of what the universe contains, it’s likelihood is raised from chance, to probable chance. Even if the odds of life were a hundred billion to one, space is more than capable of providing ample numbers of stars and planets to gamble on. Better that we use our optimism and follow these tantalising statistics, even if we’re proved wrong, than to be defeated by the magnitude of the task.

I am by no means an intelligent man and I lack a degree in anything. I’m simply lucky enough to have grasped the English language in such a way that I can make myself appear smarter. Thanks for reading.

As a former colleague of Sagan, you’re probably much more knowledgeable on him and his career, so please correct anything I say here that’s wrong.

From my humble observations, I find it that a lot of the incredibly brilliant or important people that have lived are only understood after their death. From artists, to visionaries, to even Jesus Christ, individuals who don’t seem to fit in with society are labeled as you say ‘kooks’ because no one can really understand them. I don’t want to compare him to Jesus Christ, that’s missing the point. I just wanted to say that incredibly smart people have a hard time fitting in our world.

Maybe his scientific contributions weren’t all that grand. But his contribution to the field was tremendous, because he brought so much interest to it. His love is so bittersweet. It gives me hope that our species will make a change towards living in harmony, but I think it’s just a fool’s hope.

@astrolabe
Why did you do that? Thousands or maybe millions of people love to hear what Sagan has to say, and they get much pleasure from doing so. Would you like it after your demise if someone pointed out publicly all your bad faults? Some say there is a telescope so powerful that it can see galaxy’s that are million’s maybe billions of light years away….I know for sure, that even as powerful as this telescope is, that i doubt it could find one iota, one speck, one smidgen of interest in whatever you have to say.

Those in favor of a “no life but us” argument, even when backing their stance by explanations of the true likelihood (or unlikely) of abiogenesis throughout the galaxy, really take a strange view in making their estimation.

I am not so haughty to think that the creation of life is any more grand a process than the creation of a planet itself, or a star. Given certain conditions, all matter in the universe follows the “rules” set forth, and behave accordingly. There is no fault in seeing the overwhelmingly high number of stars with potential to host a Goldilocks planet and not simply state with certainty that with the proper conditions, life will surely arise.